A six-week isoinertial (isotonic) training program was undertaken by boys (N = 26) and girls (N = 17) with ages ranging between 14 and 18 years.

Although the average strength of the boys was greater than the girls, the magnitudes of improvements were similar. For boys there was a strong linear relationship between isoinertial and isometric strength while there was none for girls. For girls, measures of isometric strength may not be a valid assessment form for isoinertial strength.

Implication. When considering strength training and assessment in adolescents, interpretations should be different for the sexes. Strength stimulation, trainability, and test performances are different for girls than boys.